Scanner and scanner data generating method

ABSTRACT

A scanner has a first mirror having a plurality of concavities configured to reflect light from a document; and a sensor configured to detect light reflected by the concavity; the concavity having an optical characteristic that differs according to position.

BACKGROUND 1. Technical Field

The present invention relates to a scanner and method of generatingscanning data.

2. Related Art

Technology for scanning documents using multiple line sensors, andcombining the output detected by each line sensor to generate scannerdata is known from the literature. For example, JP-A-2013-131794describes a configuration having multiple optical systems aligned in amain scanning direction disposed in two rows in a sub-scanningdirection, focusing by different optical systems on different linesensors, and merging the read results to generate scanning data.

The specifications of parts configuring the product are not clear in thetechnology cited above.

SUMMARY

An objective of the present invention is to provide a more desirableproduct.

To achieve the foregoing objective, a scanner according to the inventionincludes a first mirror having a plurality of concavities configured toreflect light from a document; and a sensor configured to detect lightreflected by the concavity; an optical characteristic of the concavitydiffering according to position.

This configuration enables adjusting image quality at specific locationson the path of light reflected by the concavities by adjusting anoptical characteristic of the concavity at specific positions.

In another aspect of the invention, the optical characteristic may be aspatial frequency characteristic to displacement of the document from areference position.

This configuration enables adjusting image quality at specific locationson the path of light reflected by the concavities by adjusting thespatial frequency characteristic of the concavity at specific positions.

In another aspect of the invention, the distribution of the spatialfrequency characteristic on an edge side of the concavity shifts to adocument separation side more than the distribution of the spatialfrequency characteristic on the center side of the concavity.

This configuration enables suppressing, at the edge side of theconcavity, a drop in image quality due to separation of the documentfrom the reference position.

In another aspect of the invention, the maximum of the spatial frequencycharacteristic on an edge side of the concavity is less than the maximumof the spatial frequency characteristic on a center side of theconcavity.

In this configuration, the spatial frequency characteristic isrelatively higher at the center side of the concavity than at the edgeside.

In another aspect of the invention, the optical characteristic is afocal length.

This configuration enables adjusting image quality at specific locationson the path of light reflected by the concavities by adjusting the focallength of the concavity at specific positions.

In another aspect of the invention, the focal length at an edge side ofthe concavity is longer than the focal length at a center side of theconcavity.

This configuration enables suppressing, at the edge side of theconcavity, a drop in image quality due to separation of the documentfrom the reference position.

Other objects and attainments together with a fuller understanding ofthe invention will become apparent and appreciated by referring to thefollowing description and claims taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a scanner.

FIG. 2 illustrates the configuration around the conveyance mechanism ofthe scanner.

FIG. 3 illustrates the configuration of an optical system of thescanner.

FIG. 4 schematically illustrates image reduction by the optical system.

FIG. 5 describes data synthesis.

FIG. 6 illustrates the optical system of a first reading unit.

FIG. 7 schematically illustrates the shape of the concavities of thefirst mirror.

FIG. 8 is a graph showing the simulated results of the spatial frequencycharacteristic near the center of the concavity.

FIG. 9 is a graph showing the simulated results of the spatial frequencycharacteristic near the edges of the concavity.

FIG. 10 is a flow chart of the scanning process.

DESCRIPTION OF EMBODIMENTS

A preferred embodiment of the present invention is described below inthe following order: (1) scanner configuration, (2) optical systemconfiguration, (2-1) spatial frequency characteristics, (3) scanningprocess, (4) other embodiments.

(1) Scanner Configuration

FIG. 1 is a block diagram of a scanner 1 according to this embodiment ofthe invention. The scanner 1 includes a controller 10, conveyance device40, communicator 70, operating unit 80, computer 90, and a 2-channelreading unit (including light sources, sensors, and optical units). Thecontroller 10 includes a recording medium not shown, and a processorthat reads and executes a program from the recording medium. Theprocessor may be a dedicated circuit device such as an ASIC embodied bycircuits executing a specific process, or a CPU and ASIC that worktogether.

The controller 10 controls parts of the scanner 1, and generatesscanning data based on output from a reading unit. An operating unit 80includes an output unit that provides information to the user, and aninput unit for receiving input from the user. The controller 10 controlsthe operating unit 80 to display on the output unit information forselecting scanning conditions and instructing scanning, for example.Based on output from the output unit, the user can select scanningconditions and input start-scanning commands.

When a start-scanning command is input, the controller 10 controls partsof the scanner 1 to execute the operations for scanning a document (suchas conveying the document). When scanning data is output from thereading unit by this operation, the controller 10 generates scanningdata.

The communicator 70 is a device for communicating with an externaldevice (an external computer 90 in this example), and the controller 10can send desired information to the computer 90 and receive instructionsand information from the computer 90.

In this embodiment of the invention, when the controller 10 producesscanning data, the controller 10 sends the scanning data through thecommunicator 70 to the computer 90. The scanning data may obviously beused in many ways, and may be stored on a recording medium not shown ofthe scanner 1, stored on a removable recording medium, or sent throughthe communicator 70 to a device other than the computer 90.

The scanner 1 according to this embodiment has both an automaticdocument feeder (ADF) not shown, and a scanning platen, and documentsare scanned at the scanning position regardless of which is used. Thescanner 1 according to this embodiment has a first reading unit and asecond reading unit. The first reading unit can scan both movingdocuments (the front or first side) that are conveyed by the ADF, andstationary documents that are placed by the user directly on thescanning platen. The second reading unit can scan moving documents (theback or second side, the opposite side as the front), and cannot scanstationary documents.

The first reading unit includes, as shown in FIG. 1, a first sensor 21,a first light source 31, a sub-scanning device 41, and a first opticalsystem 51. The sub-scanning device 41 is a device for moving the firstsensor 21, first light source 31, and first optical system 51bidirectionally in the sub-scanning direction.

The second reading unit includes, as shown in FIG. 1, a second sensor22, a second light source 32, and a second optical system 52, and doesnot have a device equivalent to the sub-scanning device 41. Morespecifically, the second sensor 22, second light source 32, and secondoptical system 52 are stationary inside the scanner 1. Light from thesecond light source 32 is emitted to a specific position in theconveyance path of the moving document, and light from the movingdocument passes through the second optical system 52 and is sensed bythe second sensor 22 to image the document.

The first sensor 21 and second sensor 22 comprise multiple sensor chips.Each sensor is therefore a sensor group. Each sensor chip forms a linesensor, which is a sensor extending in one direction, and comprisesnumerous photoelectric conversion elements arrayed in the one direction.In this embodiment, each sensor chip has photoelectric conversionelements arranged in three rows, and a red (R), green (G), and blue (B)color filter is respectively disposed to the photoelectric conversionelements in each row. In this embodiment of the invention, the directionin which the rows of photoelectric conversion elements extend isperpendicular to the sub-scanning direction (the conveyance direction ofa moving document). The direction in which the photoelectric conversionelements are arrayed is referred to as the main scanning direction.

The multiple sensor chips of the first sensor 21 are disposed at aspecific interval in the main scanning direction.

The multiple sensor chips of the second sensor 22 are disposedadjacently in the main scanning direction, and the interval betweenadjacent photoelectric conversion elements in different sensor chips isthe same as the interval between photoelectric conversion elements in asensor chip at a different position. In the second sensor 22, therefore,the multiple sensor chips are arrayed adjacently, and effectively form aline sensor for scanning one line in the main scanning direction.

The first light source 31 and second light source 32 each have a lampthat emits light to a scanning area (exposure position) in theconveyance path of the moving document. When a document is scanned as astationary document, the exposure position moves in the sub-scanningdirection. Light reflected from the object (a document or whitecalibration plate, for example) located at the exposure position isreceived by the sensor chips of the first sensor 21 or second sensor 22,and the sensor chips generate signals corresponding to the amount oflight received by each photoelectric conversion element.

The first sensor 21 and second sensor 22 have an analog front end, notshown. The analog front end includes a circuit that applies gain to thesignals output by the photoelectric conversion elements according to theamount of light received, and an analog/digital conversion (ADC)circuit. The analog front end in this example also has a recordingmedium for recording information indicating the gain, and the analogfront end, based on the gain information, adjusts the gain of the blacklevel of the first sensor 21 and second sensor 22 to the lowest outputvalue, and the white level to the highest output level.

Note that in this embodiment the first light source 31 and second lightsource 32 are light sources that output white light. Because thephotoelectric conversion element arrays of the first sensor 21 andsecond sensor 22 are equipped with RGB color filters, the first sensor21 and second sensor 22 can generate RGB scanning data based on thelight from a document exposed to white light.

The conveyance device 40 is a mechanism that conveys documents. Theconveyance device 40 conveys the moving document to the position exposedto light from the first light source 31, and the position exposed tolight from the second light source 32, and then conveys the movingdocument out from the scanner 1.

FIG. 2 schematically illustrates the conveyance path of the conveyancedevice 40. The conveyance path comprises plastic members not shownforming the path of the moving document, and a moving document isconveyed through the conveyance path by opposing conveyance rollers 40a, 40 b disposed at multiple positions along the path. The conveyancepath is indicated by the curve of the heavy solid line in FIG. 2. Theexposure positions on the conveyance path are indicated by the dottedlines, and one line in the main scanning direction (directionperpendicular to the X-axis and Z-axis) is read at the exposure positionby the first sensor 21 and second sensor 22.

FIG. 2 schematically illustrates the conveyance path of the conveyancedevice 40. The conveyance path comprises plastic members not shownforming the path of the moving document, and a moving document isconveyed through the conveyance path by opposing conveyance rollers 40a, 40 b disposed at multiple positions along the path. The conveyancepath is indicated by the curve of the heavy solid line in FIG. 2. Theexposure positions on the conveyance path are indicated by the dottedlines, and one line in the main scanning direction (directionperpendicular to the X-axis and Z-axis) is read at the exposure positionby the first sensor 21 and second sensor 22.

Light from the area of one line on a document is therefore split intolight from multiple areas of which the ends in the main scanningdirection overlap, and each of the split light beams is focused on asensor chip. As a result, in this embodiment of the invention, theoutput from the sensor chips of the first sensor 21 must be synthesizedto generate one line of scanning data. A merging mark used as an indexfor synthesizing data is therefore formed on the calibration plate 61 inthis embodiment of the invention.

The merging mark is formed at a position where areas overlap at the endsof adjacent areas, and by scanning the merging mark when a document isnot on the platen, the photoelectric conversion elements that read thesame position can be identified in the output of the sensor chips.

The calibration plate 61 includes a white calibration plate and a blackcalibration plate for gain adjustment, the white level is determinedbased on the result measured with the white calibration plate, and theblack level is determined based on the result measured with the blackcalibration plate. Note that the calibration plate 61 may be configuredwith a moving part, and disposed so that the target selected from amongthe merging mark, white calibration plate, and black calibration plateis moved by the moving part and set to the exposure position.

Like calibration plate 61, calibration plate 62 also has a whitecalibration plate and a black calibration plate.

In FIG. 2, the sub-scanning device 41 is a device capable of moving thefirst unit U1 bidirectionally in the sub-scanning direction (X-axis).When scanning a moving document, the sub-scanning device 41 sets thefirst unit U1 to a defined position as shown in FIG. 2. The document isthen scanned with the first unit U1 at this specific position.

When scanning a stationary document set on the scanning platen T (thatis, when scanning on a flat bed), the sub-scanning device 41 moves thefirst sensor 21, first light source 31, and first optical system 51 inthe sub-scanning direction to scan the document. In the case of astationary document, therefore, the area indicated in FIG. 2 by thedotted line and the dot-dash line connected to the dotted line is theexposure position (the document scanning range), and the exposureposition can move in the sub-scanning direction.

The second sensor 22, second light source 32, and second optical system52 of the second reading unit are disposed in the second unit U2 shownin FIG. 2. When scanning a moving document, one side (the front) is readby the first unit U1, and the other side (the back) is read by thesecond unit U2 when necessary. In this embodiment of the invention, thesecond reading unit (second unit U2) is a CIS (contact image sensor).

The first optical system 51 includes an optical member for reducing andconverging an image of the document on the first sensor 21. Morespecifically, the first optical system 51 has a member forming anoptical path guiding, to the sensor chip, light from the documentproduced by the first light source 31 emitting light to the document.The optical path may be configured in many ways, and can be configuredfrom combinations of various members, including an aperture member,lenses, and mirrors.

FIG. 3 shows an example of an optical path as viewed parallel to themain scanning direction. The configuration in FIG. 3 shows the firstlight source 31 that emits light to the document P, first optical system51, and first sensor 21. The first optical system 51 uses aconfiguration that includes a first mirror 51 a with multipleconcavities, a second mirror 51 b with multiple concavities, and anaperture member 51 c having multiple openings that function asapertures; and guides the light to the sensor chip 21 a by splitting thelight from one line in the main scanning direction of the document P(the direction perpendicular to the X-axis and Z-axis) into multipleareas that overlap in part in the main scanning direction, and reducingthe image of each area.

FIG. 4 schematically illustrates the operation of the optical systemwith the main scanning direction on the horizontal axis. In FIG. 4,light from the document P passes the first optical system 51 and isguided to the sensor chip 21 a, and the path of light from the documentP is indicated schematically by the dotted lines and dot-dash lines. Inother words, the sensor chip 21 a extends in the main scanning direction(Y-axis), and images of adjacent parts of the document P that partiallyoverlap in the main scanning direction are reduced in the parts of thefirst optical system 51 corresponding to those parts of the document P.The images from each area of the document P are then focused on thesensor chip 21 a corresponding to those parts. More specifically, animage of the area of length L in the main scanning direction is focusedon a sensor chip 21 a of length d.

That one-to-one imaging optics that form images on the second sensor 22without reducing the size are used in the second optical system 52. Thecontroller 10 therefore does not need to apply the synthesizing processto the output of the second sensor 22, and applies another imagingprocess (such as cropping or edge enhancement) to acquire the scanningdata.

However, because the first sensor reads same positions on the document Pmultiple times, the controller 10 must synthesize data output fromadjacent sensor chips where the outputs coincide to generate thescanning data. More specifically, the controller 10, based on the readresults of the merging mark formed on the calibration plate 61,superimposes the outputs of the sensor chips 21 a. More specifically, asshown in FIG. 4, the first sensor 21 is embodied by multiple sensorchips 21 a, and the multiple sensor chips 21 a are disposed to differentpositions.

When the same positions are read by different sensor chips 21 a, thesame positions are read at the ends of the sensor chips 21 a. Becausethese same positions are where the merging marks are disposed on thecalibration plate 61, when the merging mark is read without a documentpresent, each sensor chip 21 a outputs data capturing the merging mark.FIG. 5

FIG. 5 schematically illustrates the photoelectric conversion elementsof the sensor chip 21 a, the black dots denoting the photoelectricconversion elements. In FIG. 5, the merging mark is a line extending inthe sub-scanning direction, and the areas around the merging mark arewhite.

The merging mark is read by each pair of adjacent sensor chips 21 a. InFIG. 5, the photoelectric conversion elements of the sensor chips 21 athat read the merging mark are indicated by black dots, the merging markis indicated by hatching, and the photoelectric conversion elements thatread the merging mark are shown overlapping. One of the adjacent sensorchips 21 a is located on the top left side, the other is located on thebottom right side, and the sensor chips 21 a are shown schematically sothat the photoelectric conversion elements that read the merging markare vertically aligned. One of the two adjacent sensor chips 21 a isreferred to below as first sensor chip 21 a 1, and the other as secondsensor chip 21 a 2.

The first sensor chip 21 a 1 and second sensor chip 21 a 2 output, asserial data, signals corresponding to the amount of light detected bythe photoelectric conversion elements aligned in the main scanningdirection. In this example, the controller 10 analyzes the output of thefirst sensor chip 21 a 1, and determines that the merging mark wasdetected by the fifth and sixth photoelectric conversion elements E5, E6from the end. The controller 10 also analyzes the output of the secondsensor chip 21 a 2, and determines that the merging mark was detected bythe fourth and fifth photoelectric conversion elements E4, E5 from theend. In this case, the controller 10 determines that the fifth and sixthphotoelectric conversion elements E5, E6 of the first sensor chip 21 a1, and the fourth and fifth photoelectric conversion elements E4, E5 ofthe second sensor chip 21 a 2, read the same position, and in memory notshown stores the locations of the corresponding elements in each sensorchip 21 a.

The controller 10 applies the above process sequentially from the end ofthe sensor chips 21 a in the main scanning direction, and identifies thelocation of the photoelectric conversion elements that read the sameposition in each sensor chip 21 a. Note that of the multiple sensorchips 21 a embodying the first sensor 21, any of the sensor chips otherthan the sensor chips at the ends may be either a first sensor chip 21 a1 or a second sensor chip 21 a 2.

For example, if one sensor chip 21 a is the first sensor chip 21 a 1 andthen becomes the adjacent second sensor chip 21 a 2 such that the secondsensor chip 21 a 2 is treated as the first sensor chip 21 a 1, thesensor chip 21 a adjacent thereto on the opposite side becomes thesecond sensor chip 21 a 2.

Once the locations of the photoelectric conversion elements reading thesame position are determined as described above, the next time adocument P is scanned, the controller 10 generates one line of scanningdata by synthesizing the outputs of the sensor chips 21 a based on theirrespective positions.

(2) Optical System Configuration

In the configuration described above, a segmented reduction opticssystem that reduces a document through multiple optical paths andfocuses on multiple sensor chips 21 a is used for the first readingunit, and the second reading unit is a CIS that scans a document usingmultiple sensor chips and a 1:1 (same size) imaging optical system. As aresult, different optical systems are used in the first reading unit andthe second reading unit.

FIG. 6 illustrates the parts related to one optical path in the firstoptical system 51 of the first reading unit. As shown in FIG. 6, lightfrom a document P passes the concavity of the first mirror 51 a, throughthe aperture of the aperture member 51 c, and is focused on the sensorchip 21 a through the concavity of the second mirror 51 b.

In this configuration, the optical characteristics of the concavity ofthe first mirror 51 a differ according the position. FIG. 7schematically illustrates the shape of the concavity of the first mirror51 a. FIG. 7 is a section view of the concavity on a plane through thefocal points of the first mirror 51 a, and shows the shape of twoconcavities in section. Note, however, that FIG. 7 exaggerates thedifferences in the shape (curvature) according to the position of theconcavities. The actual differences in the shape due to the position ofthe concavities is extremely minute.

The concavities of the first mirror 51 a in this embodiment havedifferent optical characteristics at the edge sides and the center sideof the concavities as shown in FIG. 7. More specifically, the opticalcharacteristics in this embodiment can be expressed by the focal length,and the focal length at the edge side of the concavities is longer thanthe focal length in the center of the concavity. To better illustratethis difference, FIG. 7 exaggerates the difference between the edges andthe center, and emphasizes the border between the edge area and thecenter. In practice, the change between the edge area and the center isless than shown in FIG. 7, and the boundary between the edge area andthe center is smooth so that the image does not change suddenly at theboundary. The edge area and the center may transition smoothly overall.

Note that the edge and center sides of the concavity are defined as theyrelate to the main scanning direction when the part converging light ona single sensor chip 21 a is treated as a single concave mirror. Inother words, the area that reflects light converging in the center ofthe sensor chip 21 a in the main scanning direction can be defined asthe center side, and the area that reflects light converging at the edgeof the sensor chip 21 a in the main scanning direction can be defined asthe edge side. In FIG. 7, the part at the bottom of the concavity isdefined as the center side. Also in FIG. 7, the first mirror 51 a isformed by joining multiple concave mirrors side by side in the mainscanning direction, but the location of the boundary is not limited tothe locations shown in the example in FIG. 7. For example, aconfiguration in which the mirrors are joined at position P1 in FIG. 7is also conceivable. Even in this configuration, the locations of thecenter and edge sides are defined as shown in FIG. 7.

In FIG. 7, the focal point of the center side of the concavity is focalpoint Fc, and the focal point of the edge side of the concavity is focalpoint Fe. As shown in FIG. 7, in this example the focal length of thecenter side of the concavity is Lc, the focal length of the edge side ofthe concavity is Le, and focal length Le of the edge side of theconcavity is longer than the focal length Lc of the center side of theconcavity. As described above, the optical characteristics of theconcavity of the first mirror 51 a in this embodiment differ accordingto the position, and image quality is adjusted according to the positionof the optical path.

In this embodiment of the invention, the optical characteristic thatdiffers according to the position on the concavity of the first mirror51 a is the focal length, and the focal length at the edge side of theconcavity is longer than the focal length at the center side of theconcavity. A drop in image quality due to separation of the documentfrom the platen glass at the edge side of the concavity can besuppressed better than a drop in image quality at the center side of theconcavity. Note that the curvature of the concavity at the edge sidedoes not need to be the same as the curvature of the concavity at thecenter side. For example, a configuration that gradually changes thecurvature from the center side to the edge side may be used.

(2-1) Spatial Frequency Characteristics

As described above, the optical characteristics of the first mirror 51 ain this embodiment differ according to the position, but the opticalcharacteristic may refer to various properties other than the focallength. For example, the spatial frequency characteristic may be used asthe optical characteristic. More specifically, when the spatialfrequency of light reflected from a concavity and picked up by the eyeor a sensor varies according to the position on the concavity, theoptical characteristics may be said to differ according to the positionon the concavity. In this way, a configuration in which the spatialfrequency varies according to the position on the concavity can also beseen as a configuration enabling adjusting the image quality accordingto the position of the concavity.

FIG. 8 and FIG. 9 show the results of simulations of the spatialfrequency characteristics acquired by scanning a document with the firstreading unit. The path of light from a document P was simulated based onthe shape and size of the actual members of a first optical system 51configured as shown in FIG. 6, and a process acquiring the spatialfrequency characteristics with varying amounts of separation of thedocument P from the platen glass (reference position) was executed. Thegraphs shown in FIG. 8 and FIG. 9 were then created based on the spatialfrequency characteristics (MTF: Modulation Transfer Function) acquiredat the different amounts of separation.

Note that FIG. 8 shows the spatial frequency at the center side of theconcavity, and FIG. 9 shows the spatial frequency at the edge side ofthe concavity. Both graphs show the results of simulations where theequivalent f-number of the first optical system 51 is 8.6 and 16.6, thesolid line based on data for an equivalent f-number of 8.6, and thedotted line based on data for an equivalent f-number of 16.6. Theequivalent f-number is the value acquired by simulating the f-numbersupposing a lens forming an optical path equivalent to the optical pathformed by the optical system. In FIG. 8, document separation ranged from−5 mm to 5 mm (a negative value was included for simulation), and inFIG. 9 document separation ranged from −5 mm to 8 mm.

FIG. 8 and FIG. 9 also show the spatial frequency of a CIS (such as thesecond reading unit) with a typical f-number of approximately 2 to 3.Compared with a CIS, the width of the spatial frequency distributionwith the first reading unit using the first optical system 51 isgreater, and the spatial frequency characteristic exceeds 50% over awide range. Therefore, the first reading unit can suppress a drop inimage quality due to separation of the document from the platen glassbetter than the second reading unit.

Note that because barcodes and QR codes (R) can be read if the spatialfrequency characteristic exceeds 50%, tolerance for separation of thedocument from the reference position is poor at less than 1 mm with aCIS, but such symbols can be read by the first optical system 51 even ifthe document separates several millimeters from the reference position.

In addition, as shown in FIG. 8, distribution of the spatial frequencycharacteristic in the center side of the concavity is substantiallyleft-right symmetrical to the center at a document separation of 0 mm.

As shown in FIG. 9, however, the center of the distribution of thespatial frequency characteristic at the edge side of the concavity is ata document separation of approximately 1 to 2 mm, and is shifted to thedocument separation side from 0 mm of document separation. Morespecifically, the distribution of the spatial frequency characteristicat the edge side of the concavity shifts to the document separation sidefrom the distribution of the spatial frequency characteristic at thecenter side of the concavity. As a result, even if there is greaterdocument separation at the edge side of the concavity than at thecenter, a drop in image quality due to separation of the document fromthe reference position can be suppressed.

The maximum of the spatial frequency characteristic at the edge side ofthe concavity is less than the maximum of the spatial frequencycharacteristic at the center side of the concavity. For example, atequivalent f-number 8.6, the maximum of the spatial frequencycharacteristic at the edge side of the concavity is Cmax as shown inFIG. 8, and the maximum of the spatial frequency characteristic at thecenter side of the concavity is Emax as shown in FIG. 9.

Because Cmax>Emax as will be understood from FIG. 8 and FIG. 9, themaximum of the spatial frequency characteristic at the edge side of theconcavity is less than the maximum of the spatial frequencycharacteristic at the center side of the concavity. Therefore, isreducing the maximum of the spatial frequency characteristic is allowed,a relatively greater spatial frequency characteristic can be achieved inthe center side of the concavity than at the edge side of the concavity,and a drop in image quality due to document separation can beeffectively suppressed at the edge side of the concavity.

(3) Scanning Process

The scanning process in this embodiment of the invention is describednext with reference to the flow chart in FIG. 10.

When the user directly or indirectly selects the document scanningresolution and paper feed method (ADF or document platen), and commandsscanning to start, the controller 10 receives the scan command andstarts the scanning process shown in FIG. 10. When the scanning processstarts, the controller 10 gets the scanning settings, including thedocument scanning resolution and the paper feed method (step S100). Notethat in this example the user can select and set the desired resolutionfrom among the plural document scanning resolutions that can be set forreading light reflected from a moving document.

Next, the controller 10 measures image shading. More specifically, thelowest level of light detectable by the sensor chip is the black level,and the highest level of detectable light is the white level, but theblack level and white level can vary according to the sensor, lightsource, and other characteristics. For example, sensor characteristicsmay vary due to noise such as dark current, sensor manufacturing errors,and aging, and the black level and white level can vary according tosuch variations. Therefore, to scan with high quality, imaging shadingis preferably measured before reading a document to determine at leastone of the black level and white level.

The controller 10 in this example first measures the white level (stepS105). More specifically, before reading the document, the controller 10controls the first reading unit (and the second reading unit if scanningboth sides) to read the white calibration plate of the calibration plate61. As a result, because output indicating the measurement acquired bythe first sensor 21 (and the second sensor 22 if scanning both sides)from the white calibration plate is acquired, the controller 10 acquiresthe output as the white level.

Next, the controller 10 measures the black level (step S110). Morespecifically, before reading the document, the controller 10 controlsthe first reading unit (and the second reading unit if scanning bothsides) to read the black calibration plate of the calibration plate 61.As a result, because output indicating the measurement acquired by thefirst sensor 21 (and the second sensor 22 if scanning both sides) fromthe black calibration plate is acquired, the controller 10 acquires theoutput as the black level.

Next, the controller 10 measures the merging mark (step S115). Morespecifically, before scanning the document, the controller 10 controlsthe first reading unit to scan the merging mark of the calibration plate61. As a result, the results of scanning the merging mark are outputfrom the multiple sensor chips of the first sensor 21. Note that becausethere is no need to synthesize the output of the second sensor 22 inthis embodiment, the merging mark is not scanned by the second sensor22.

Next, the controller 10 identifies the photoelectric conversion elementsthat read the same position (step S120). For example, using the examplein FIG. 5, the controller 10 identifies photoelectric conversionelements E5, E6 of the first sensor chip 21 a 1, and photoelectricconversion elements E4, E5 of second sensor chip 21 a 2, as thephotoelectric conversion elements that read the same position. Thecontroller 10 executes the same process for each sensor chip 21 a, andidentifies the photoelectric conversion elements in each sensor chipthat read the same position.

Next, the controller 10 sets the black level and white level (stepS125). That is, the controller 10, based on the white level measured instep S105 and black level measured in step S110, sets the white leveland black level for each photoelectric conversion element. Morespecifically, based on the white level measured in step S105 and blacklevel measured in step S110, the control unit 13 sets the gain to enablemeasuring gradations between the white level and black level in theeffective detection range.

Next, the controller 10 determines if the paper supply method is by ADFor not (step S130). More specifically, the controller 10 references thescanning settings acquired in step S100 to determine if the paper supplymethod is by ADF or using the scanning platen. If the controller 10determines in step S130 that the paper supply method is not by ADF, thatis, that a document on the document platen is to be scanned, thecontroller 10 starts sub-scanning (step S135). More specifically, thecontroller 10 outputs a control signal to the sub-scanning device 41 tomove the first sensor 21, first light source 31, and first opticalsystem 51 in the sub-scanning direction.

The controller 10 reads the document during the sub-scanning operation(step S140). More specifically, the controller 10 controls the firstsensor 21 to read, and acquires the read results from the sensor chips21 a of the first sensor 21.

Next, the controller 10 synthesizes the output from the sensor chips 21a (step S145). More specifically, the controller 10 digitizes the outputof the sensor chips 21 a, adjusts the gain according to the white leveland black level set in step S125, executes a synthesizing processcausing the photoelectric conversion elements identified in step S120 tooutput one pixel, converts value and color, crops the document, appliesedge enhancement, and executes other signal processing operations. Theseprocesses may be applied sequentially to the line by line results readin step S140, or in a batch after all read results are acquired.

Next, the controller 10 outputs the scanning data (step S150). Morespecifically, when one page of data synthesized in step S145 isaccumulated, the controller 10 image processes the data for imagecropping and edge enhancement, for example, generates scanning data forthe one page, and outputs the scanning data through the communicator 70to the computer 90.

If the controller 10 determines in step S130 that the paper supplymethod is by ADF, the controller 10 starts conveying the document (stepS155). More specifically, the controller 10 outputs a control signal tothe sub-scanning device 41 to move the first reading unit to a specificscanning position. The controller 10 then outputs a control signal tothe conveyance device 40 to convey the document through the conveyancepath.

While the document is being conveyed, the controller 10 reads thedocument (step S160). More specifically, the controller 10 controls thefirst sensor 21 to read, and acquires the read results from the sensorchips 21 a of the first sensor 21. Note that if duplex scanning isselected in step S100, the controller 10 also controls the second sensor22 to read, and acquires the read results from the second sensor 22.

Next, the controller 10 signal processes the output (step S165). Morespecifically, the controller 10 digitizes the output of the sensor chips21 a (including the output from the second sensor 22 if duplex scanningis selected), adjusts the gain according to the white level and blacklevel set in step S125, executes a synthesizing process causing thephotoelectric conversion elements identified in step S120 to output onepixel, converts value and color, crops the document, applies edgeenhancement, and executes other signal processing operations. Theseprocesses may be applied sequentially to the line by line results readin step S160, or in a batch after all read results are acquired. Notethat because there is no need to synthesize the read results from thesecond sensor 22, the read results from the second sensor 22 are notsubject to the synthesis process.

Next, the controller 10 outputs the scanning data (step S170). Morespecifically, when one page of data synthesized in step S165 isaccumulated, the controller 10 applies image processing includingcropping and edge enhancement, for example, generates scanning data forthe one page, and outputs the scanning data through the communicator 70to the computer 90. If duplex scanning was selected, the controller 10generates the scanning data using the one page of data synthesized instep S165 and the one page of data read from the back in step S160, andthen outputs to the computer 90.

(4) Other Embodiments

The invention is described with reference to desirable embodimentsabove, but the invention is not so limited and can be varied in manyways. For example, the scanner described above may be a component of amultifunction device, which is an electronic device that is also usedfor other purposes.

The merging mark may also be configured in many ways, and may be twolines or graphic of another shape. During synthesis, images may also besynthesized to eliminate deviation (such as skewing) of the sensor chipsin the sub-scanning direction.

To superimpose the outputs of photoelectric conversion elements thatread the same part of the document, a statistical value (such as theaverage) of scanning data from one sensor chip and scanning data fromthe other sensor chip may be acquired and used, or the scanning datafrom one of the sensor chips may be used.

Scanning data generated by scanning may be output to a computer 90,output and stored to a storage medium such as USB memory installed tothe device, output to a print mechanism and printed (or copied), oroutput and displayed on a monitor.

Alternatively, the final scanning data may be generated by outputting anarea detection image to a computer 90, and applying image analysis andsynthesis by a driver program or application program of the computer 90.In this configuration, the computer 90 may be considered part of thescanner.

The first mirror may have multiple concavities reflecting light from thedocument. More specifically, the first mirror may be configured asneeded to form an optical path to the sensor group by changing thedirection of travel of light from a document by reflection. The lightfrom a document may be any light output from the document as a result ofexposing the document to light from a light source, and in manyconfigurations is reflected light, but may be fluorescent light, forexample.

The first mirror has multiple concavities. More specifically, differentoptical paths can be formed by the concavities, and light from adocument can be guided through multiple optical paths to multiplepositions (such as multiple sensor chips) corresponding to therespective optical paths.

In addition, the concavities may be configured as surfaces that reflectand converge parallel incident light on a focal point, and may besurfaces configured as an optical system (such as a reduction opticalsystem that reduces the size of the image) that changes the size of theimage corresponding to the light from a document.

The number of concavities is not limited insofar as the configuration atleast guides light from multiple areas in the main scanning direction tomultiple positions. For example, a configuration that is a numbercorresponding to the number of sensor chips in a sensor can be used.

In addition, multiple mirrors may be disposed to the same optical path.For example, a configuration that converges light through tworeflections by two concavities may be used. The focal length andcurvature of a concavity is not specifically limited, and may be changedaccording to the size of the scanner or the configuration of the opticalsystem, for example.

The sensor may be configured in any form enabling sensing lightreflected by a concavity. Photoelectric conversion elements used fordetection may be configured as a sensor chip. There may be one ormultiple sensor chips.

Note that the sensor chip has photoelectric conversion elements arrangedat least in the main scanning direction, and may also have photoelectricconversion elements at multiple positions in the sub-scanning direction.In the latter case, photoelectric conversion elements may be at multiplepositions in the sub-scanning direction in the sensor chip, or byarraying sensor chips in the sub-scanning direction, photoelectricconversion elements may be disposed at multiple positions in thesub-scanning direction.

Note that in a configuration in which photoelectric conversion elementsare at multiple positions in the sub-scanning direction, thephotoelectric conversion elements at multiple positions in thesub-scanning direction may be used to form images of different colors,or be used to form an image of one line in the main scanning directionby combining their outputs.

The optical characteristic of the concavity may be any characteristicthat affects the imaging result of the sensor, and may be a propertyother than the spatial frequency characteristic or focal length. Forexample, optical characteristics may change according to the curvatureand material of the concavity, and the type of surface (such as aparaboloid or free-form surface). The optical characteristic differsaccording to the position of the concavity, and may change in stepsaccording to the position, or change continuously.

Furthermore, an example in which the optical axis is straight isdescribed above for simplicity, but by adding mirrors to the firstoptical system and the second optical system to fold the optical pathappropriately, the overall size of the optical system may be reduced.

The invention being thus described, it will be obvious that it may bevaried in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A scanner comprising: a first mirror having aplurality of concavities configured to reflect light from a document;and a sensor configured to detect the light reflected by theconcavities, wherein an optical characteristic of the light reflected bythe concavities differs according to positions at which the light isreflected on the concavities of the first mirror, and a spatialfrequency characteristic of the light reflected by the concavitiesdiffers according to positions at which the light is reflected on theconcavities of the first mirror.
 2. The scanner described in claim 1,wherein: a distribution of the spatial frequency characteristic on anedge side of the concavities shifts to a document separation side morethan a distribution of the spatial frequency characteristic on a centerside of the concavities.
 3. The scanner described in claim 1, wherein: amaximum of the spatial frequency characteristic on an edge side of theconcavities is less than a maximum of the spatial frequencycharacteristic on a center side of the concavities.
 4. A scannercomprising: a first mirror having a plurality of concavities configuredto reflect light from a document; and a sensor configured to detect thelight reflected by the concavities, wherein an optical characteristic ofthe light reflected by the concavities differs according to positions atwhich the light is reflected on the concavities of the first mirror, anda focal length of the light reflected by the concavities differsaccording to positions at which the light is reflected on theconcavities of the first mirror.
 5. The scanner described in claim 4,wherein: the focal length at an edge side of the concavities is longerthan the focal length at a center side of the concavities.
 6. A methodof generating scanning data using a sensor configured to reflect lightfrom a document by a first mirror having a plurality of concavities, anddetect the light reflected by the concavities, comprising: detecting thelight which is reflected by the concavities and whose opticalcharacteristic, spatial frequency characteristic or focal length differsaccording to positions at which the light is reflected on theconcavities of the first mirror, and generating scanning data by thesensor.